c使用fstat问题比较文件大小

Question

比较2个文件大小的代码似乎表现得好像keyfile> sourcefile。下面的代码中是否缺少某些内容，我可以更改哪些内容？我用于测试的两个文件是3kb密钥文件和14kb源文件，它们应该激活下面提供的最后一个if语句。

/* Get size of sourcefile. */
if((sourcefile = fopen(argv[1], "rb"))== NULL)
{
printf("Can't open source file.\n");
printf("Please enter a valid filename.\n");
printf("USAGE: OTP <source file> <output file> <keyfile>\n");
return (1);
}

fflush(sourcefile);
fstat(fileno(sourcefile), &statbuf);
fclose(sourcefile);

/* Get size of keyfile. */
if((keyfile = fopen(argv[3], "rb"))== NULL)
{
printf("Can't open keyfile.\n");
printf("Please enter a valid filename.\n"); 
printf("USAGE: OTP <source file> <output file> <keyfile>\n");
return(1);

fflush(keyfile);
fstat(fileno(keyfile), &keybuf);
fclose(keyfile);
}

/* Open necessary files. */
keyfile=fopen(argv[3], "rb");
sourcefile=fopen(argv[1], "rb");
destfile=fopen(argv[2], "wb");

/* Check if keyfile is the same size as, or bigger than the sourcefile */
if((keybuf.st_size) < (statbuf.st_size))
{
printf("Source file is larger than keyfile.\n");
printf("This significantly reduces cryptographic strength.\n");
printf("Do you wish to continue? (Y/N)\n");
scanf("%c", &ans);
if(ans == 'n' || ans == 'N')
    {
    return (1);
    }
if(ans == 'y' || ans == 'Y')
    {
    printf("Proceeding with Encryption/Decryption.\n");
    }
}   

Answer 1

这是因为如果无法打开密钥文件，你只需要fstat。移动你的大括号。此外，作为表单的优化，不要打开文件，统计它，关闭它并重新打开它。只是不要关闭它继续。

所以，既然你问过

/* Get size of sourcefile. */
if((sourcefile = fopen(argv[1], "rb"))== NULL)
{
printf("Can't open source file.\n");
printf("Please enter a valid filename.\n");
printf("USAGE: OTP <source file> <output file> <keyfile>\n");
return (1);
}

fflush(sourcefile);
//fstat(fileno(sourcefile), &statbuf);   // <-- this is not needed
//fclose(sourcefile);                    // <-- this is not needed

/* Get size of keyfile. */
if((keyfile = fopen(argv[3], "rb"))== NULL)
{
printf("Can't open keyfile.\n");
printf("Please enter a valid filename.\n"); 
printf("USAGE: OTP <source file> <output file> <keyfile>\n");
return(1);
    }                                     // <-- this brace is new (well, moved) (1)

fflush(keyfile);
//fstat(fileno(keyfile), &keybuf);    // <-- not needed
//fclose(keyfile);                    // <-- not needed
//}                                     // <-- this brace has moved up 4 lines to (1)

/* Open necessary files. */
keyfile=fopen(argv[3], "rb");
sourcefile=fopen(argv[1], "rb");
destfile=fopen(argv[2], "wb");

/* Check if keyfile is the same size as, or bigger than the sourcefile */
if((keybuf.st_size) < (statbuf.st_size))
{
printf("Source file is larger than keyfile.\n");
printf("This significantly reduces cryptographic strength.\n");
printf("Do you wish to continue? (Y/N)\n");
scanf("%c", &ans);
if(ans == 'n' || ans == 'N')
    {
    return (1);
    }
if(ans == 'y' || ans == 'Y')
    {
    printf("Proceeding with Encryption/Decryption.\n");
    }
}